The present invention pertains to azeotropic and azeotrope-like compositions of 1-chloro-1,3,3,3-tetrafluoropropane (HCFC-244fa) and hydrogen fluoride.
In recent years there has been universal concern that completely halogenated chlorofluorocarbons (CFC""s) might be detrimental to the Earth""s ozone layer. Consequently, there is a worldwide effort to use fluorine-substituted hydrocarbons that contain fewer or no chlorine substituents. In this regard, 1,1,1,3,3-pentafluoropropane, a hydrofluorocarbon (HFC) having zero ozone depletion potential, is being considered as a replacement for chlorofluorocarbons such as dichlorodifluoromethane in refrigeration systems and trichlorofluoromethane as a blowing agent. The production of HFC""s, i.e. compounds containing only carbon, hydrogen and fluorine has been the subject of interest to provide environmentally desirable products for use as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions and power cycle working fluids. It is known in the art to produce fluorocarbons such as HFC""s by reacting hydrogen fluoride with various hydrochlorocarbon compounds. Such HFC""s are not only considered to be much more environmentally advantageous than hydrochlorofluorocarbons (HCFC""s) or chlorofluorocarbons (CFC""s) because they are not non-ozone depleting, but also they are also non-flammable, and non-toxic as compared to the chlorine containing compounds.
1,1,1,3,3-Pentafluoropropane (HFC-245fa) is well known in the art as described in U.S. Pat. Nos. 5,496,866 and 5,574,192, both of which are incorporated by reference herein in their entirety.
It has now been found that an intermediate in the production of substantially pure HFC-245fa, is an azeotropic or azeotrope-like mixture of 1-chloro-1,3,3,3-tetrafluoropropane (HCFC-244fa) and hydrogen fluoride. The azeotropic and azeotrope-like compositions find use not only as intermediates in the production of HFC-245fa, but they are additionally useful as nonaqueous etchant mixtures for etching semi conductors in the electronics industry, as well as compositions for removing surface oxidation from metals. In addition, the formation of an azeotropic or azeotrope-like composition of HCFC-244fa and hydrogen fluoride is useful in separating a mixture of HCFC-244fa and an impurity such as 1,1,1,3,3-pentachloropropane (HCC-240fa). When it is desired to separate a mixture of HCFC-244fa and an impurity, HF is added to form an azeotropic mixture of HCFC-244fa and hydrogen fluoride, and then the impurity is removed from the azeotropic mixture, such as by distillation, scrubbing or other known means.
In one embodiment, the invention provides an azeotropic composition consisting essentially of 1-chloro-1,3,3,3-tetrafluoropropane and hydrogen fluoride.
The invention further provides an azeotropic or azeotrope-like composition consisting essentially of from about 1 to about 75 weight percent hydrogen fluoride and from about 25 to about 99 weight percent 1-chloro-1,3,3,3-tetrafluoropropane, which composition has a boiling point of from about 30xc2x0 C. to about 60xc2x0 C. at a pressure of from about 10 psia to about 68 psia. In a preferred embodiment, the azeotropic or azeotrope-like compositions consist essentially of from about 15 to about 60 weight percent hydrogen fluoride and from about 40 to about 85 weight percent 1 -chloro- 1,2,2,2-tetrafluoropropane. In a more preferred embodiment, the azeotropic or azeotrope-like compositions consist essentially of from about 35 to about 40 weight percent hydrogen fluoride and from about 60 to about 65 weight percent 1 -chloro- 1,2,2,2-tetrafluoropropane.
In another embodiment, the invention provides a method of forming an azeotropic or azeotrope-like composition, which method comprises blending from about 1 to about 75 weight percent hydrogen fluoride and from about 25 to about 99 weight percent of 1-chloro-1,3,3,3-tetrafluoropropane, which composition has a boiling point of from about 30xc2x0 C. to about 60xc2x0 C. at a pressure of from about 10 psia to about 68 psia. In a preferred embodiment, the invention provides a method of forming an azeotropic or azeotrope-like composition, which method comprises blending from about 15 to about 60 weight percent hydrogen fluoride and from about 40 to about 85 weight percent of 1-chloro-1,3,3,3-tetrafluoropropane. In a more preferred embodiment, the invention provides a method of forming an azeotropic or azeotrope-like composition, which method comprises blending from about 35 to about 40 weight percent hydrogen fluoride and from about 60 to about 65 weight percent of 1 -chloro- 1,3,3 ,3-tetrafluoropropane.
In still another embodiment, the invention provides a process for removing 1-chloro- 1,3,3,3 -tetrafluoropropane from a mixture of 1 -chloro- 1,3,3,3 -tetrafluoropropane and at least one impurity, which process comprises adding hydrogen fluoride to the mixture in an amount sufficient to form an azeotropic or azeotrope-like composition of l-chloro-1,3,3,3-tetrafluoropropane and hydrogen fluoride, and thereafter separating the azeotropic composition from the impurity.